Rev. BioI. Trop., 22 ( 1 ) : 5 1-66, 1974
Sandy-beach fauna of the Pacific and Atlantic
coasts of Costa Rica and. Colombia
by
Deborah M. Dexter*
( Received for publication September 3, 197 3 )
ABSTRACT:
The macros copie infaunas of 18 tropical sandy beaches along
both coast; of Costa Rica and Colombia were examined during the spring
of 1971. The Pacific beaches averaged 7 times the density of individuals.
had significantly larger numbers of species., and had significantly finer
sand than the Atlantic beaches. The two most abundant species. the isopods
Cirolana salvadol'ensis and Exosphaeroma diminutum, occurred on both
coasts. The polychaetes Scolelepis agilis and Hemipodus a�matus were
found on the majority of beaches on both coasts. In general, the faunas
of the Pacific and Atlantic sandy beaches were composed of closely related
species.
The purpose of this study was to make a preliminary description of the
sandy-beach fauna along the Pacific and Atlantic coasts of Costa Rica and Co­
lombia. The objective was to establish species composition, abundance, and
zonation patterns for each beach, and to compare similarities and differences
among the faunas.
Studies on tropical sandy beaches are very limited. Dt..HL ( 1 ) described
worldwide zonation patterns of boreal, temperate, and tropical beaches, charac­
terizing each by three or four species of larger invertebrates, predominantly
Crustacea. Previous studies on American tropical, sand beaches are those of
RODRIGuEiZ ( 10 ) in Venezuela, Wt..DE ( 14 ) in Jamaica, and DEXTER ( 3 ) in
Panama.
*
Department of Zoology, California State University, San Diego, California 9� l i§,
u.S.A.
51
52
REVISTA D E BIOLOGIA TROPICAL
METBlODS
Beaches were selected as study sites on the basis of their accessibility
and distribution along the coastlines of Costa Rica and Colombia. Eighteen
beaches, one half on each coast, were sampled from February through May, 197 1 ;
1 3 beaches were located i n Costa Rica and 5 in Colombia. The island beaches
of San Andrés, a Colombian possesion, located in the Caribbean Sea off the
coast of Nicaragua, were depauperate in fauna.
A systematic sampling design was used. The beaches were divided into
strata, the width of which depended on the area exposed at low tide. Strata
varied from 5 to 2 0 m on the Pacific coast and from 1 to 5 m on the Atlantic.
Each beach was divided into at least 5' strata. Three or four repJicate samples,
1 m aparl, were taken in each stratum. A total of 197 samples were collected
from the Atlantic beaches and 2 37 fron the Pacific beaches. Sampling p rocedure
consisted of placing a 0.1 m2 quadrat over the sand at low tide, removing sand
to a depth of 5 cm, and sieving it through a 500 ¡;,-mesh neto Organi:ms were
separated from the sand residue by careful sorting and by floatation in a
saturated sugar solution. Sediment cores were taken at high, m id, and low' tidal
levels.
Sedimentary partic1e size was analyzed with the use of an Emery
settling tube (EMERY, 4) .
The Shannon-Wiener diversity index ( LLOYD and GHELARDl, 8 ) takes
into account both total number of species and numerical equality in species
representation, and is relatively independent of sample size, when the sample
is larger than 200 individual s (SANDERS, 1 2 ) . This index was calculated for
all beaches with a sample size greater than 2 00 individuals. The index NM
(FAGER, 5 ) is based on the number of moves neceséary to convert the observed
distribution of individuals of species into an even distribution. This index
measures the equitability of distribution of indíviduals among the sp ecies and
:was calculated for all but one beach, To determine faunal similarity among
the beaches, the percentage composition of each species for each sample locatíon
was computed. Sample pairs were compared by summing the smaIler percentages
of the species present in both samples. This value is the "index oE affinity"
which measures the p'ercent of fauna common to a pair of samples ( SANDERS
11).
,
DESCRIPTION OF COLLECTION SITES
ATLANTIC BEACHES
Síte N9 1
Isla San Andrés, Colombia; l 2°32'N, 8 lo34'W; caarse calcareous sand;
median grain size, 369 fL; 6 m wide at low tide,
Site N° 2
Playa Bonita, Limón, Costa Rica; lOoOl'N, 83°04'W; calcareous salid;
median grain size, 2 67 fL;
Site N° 3
Airport Beach,
Limón,
sand composed mainly
14 m wide at low tide.
Costa Rica;
of
9°58'N,
magnetite and
2 0 6 fL; 14 m wide at low tide .
8 30 0 l '\'V;
olivine;
basic igneous
median graio
size,
DEXTER: SANDY-BEACH FAUNA OF COSTA RICA AND COLOMBIA
Site N9 -1
Caimita North, Costa Rica;
9\i45'N,
82°)2''\'V';
bas!c
53
¡gneous
sand;
median grain size, 197 11; 25 m wide at low tide.
Sitc N9:>
Cahuita South, Costa Rica; 9°44'N, 82°50'W; c:1lc�reous sand; median
graio size, ,77 1-'-; 12 m wide at low tide.
Puerto
Vie:jo,
Costa
9°40'N,
Rica;
82°44'W;
igneous
baú
median grain size, na p.; 25 m \Vide at 10\V tide.
subtiJal
sand
abundant
:m
quil!fJuicJperfoJ"tlla lala
Site N° 7
population
Boca Grande, Cartagena
Pradomar,
Puerto
tlle
sand
dallar
MeJlitfl
was presento
roo30'N; 75°40'W; acidic igncous
Colombi¡t;
,
saod; median graio size, 165 fA-; 18
5ite N° 8
of
sand;
In the ncarby
Colombia,
\Vide at low tide.
!TI
Colombia;
1 tOOS'N,
75a09'W;
basic
igneous sand; median graio size, 231 p.; 6 m wide at 10\V tick
$ite NII 9
Rodadero,
Santa Marta,
11015'N,
Colombia;
74°13'W;
mixcd acidic
and oosic igneous sand; median graio size, 323 /1.,; 5 m \Vide at 10\V
ti de.
PACIFIC BE_"-CHES
5itc N° 1
Playita Blanca, Coco, Costa Rica; IOo34'N, 85°42'\'{T; calcareous sand;
median grain size, 283 fA-; 30
Sitc NO) 2
5itc N° 3
Tamarindo,
In
wide at low tide
lOoJ9'N,
Costa Rica;
85°50'\\:';
quartz/fe!dspar
amounts
of
s ize, 1 37
1'; 90 m wide at low tide.
calcareous
and
.
mixed saod with
particles;
equal
medi an grain
Sámara, Costa Rica; 9059'N, 85°3S'W; quartz sand; median grain sizc,
151 fA-; 130 m wide at low tid e.
Site N° 4
Puntarenas (La Punta), Costa Rica; 9°59'N, 84°45W; volcanic sand;
median grain size, 232 p.; 60 m wide at low tidC'.
5ite N'I 5
Boca de Barranca,
Costa
Rica;
9t158'N,
S4°45'W;
bcach
locatcd
at
th� mouth of a small river; voleanic sandj median gr�in size, 216 ¡t;
SO m y.,j¿c at low t:<le.
$itc N° 6
Jacó,
Costa
185
size,
Sitc NQ 7
Playa
with
/1.;
Cocal,
9°37'N,
m
180
Quepos,
considerable
located oear
Sitc NQ 8
Rica;
Costa
Jow
Rica;
of
small
Quepos,
voleanic
9°26'N;
r¡ver;
Costa
sa:-:d;
median
grain
tide.
median
weathering;
mouth
Playa Espadilla,
S4°38'W;
\Vide at
g,juIO'W;
grai n
size,
voleanic sand
205
fA-;
beach
110 m wide at low tide.
Rica;
9°24'N,
84QlO'\V;
G!.kareous,
voJcanic, and quartz/fclds¡:>ar sands in approxim2tely equal amounts;
median grain size, 203 }J.; 90 m wide at low tiJe.
5ite N° 9
Juan
Chaco,
oear
mouth
of
Bahía
de
..Málága,
Colombia;
3°54'N,
77°2 2'W; basic igneous sand of altcred volcanic o1"igin; median graio
sizc, 201 f.L; 75 m w¡de- at low tide.
54
REVISTA DE BIOlOGIA TROPICAL
RESULTS
A total of 2,249 individuals from 19.7 m2 of beach were collected along
the Atlantic coast. The distribution and density of these 33 species are given
in Table 1 . A total of 1 7, 747 individua1s were collected from a samp1e area
of 23.7 m2 on the Pacific beaches. The distribution and density of these 52
species are shown in Table 2 . Tab1e 3 presents a synthesis of the number of
individua1s and number of species, area sampled, diversity index, and the per­
cent composition of the dominant species on each beach. The average index
of faunal affinity among the Atlantic beaches was 39.7 and 2 6. 5 in the Pacific
(Fig. 1 ) .
On1y 6 of the 3 3 species collected from the tropical At1antic beaches
of Costa Rica and Colombia were present on at 1east half of the beaches. These
inc1uded the isopods Cirotana salvadorensis and Aneinus brasiliensis; polychaetes
Seole/epis agilis and Hemipodus armatttS; a phoxocepha1id amphipod, and the
decapod Emerita brasiliensis. Of these, on1y C. saivad07ensis had a frequency
(presence in total quadrats) greater than 50 % ; S. agilis had a frequency grea­
ter than 20 % . These 6 species comprised 74% (by number) of the Atlantic
fauna.
Of the 52 species collected a10ng the Pacific coast, 10 were present on
at 1east ha1f of the beaches. These inc1uded the isopods Cirolana salvadorensis
and Exosphaeroma diminutum; the po1ychaetes Seolelepis agilis, Hemipodus
armatus, and NePhthys singularis; a phoxocepha1id amphipod, the decapod Eme­
rita rathbunae, a bodatriid cumacean, the biva1ve Donax panamensis, and the
gastropod Olivella sem;striata. C. salvadorensis and E. diminutum had fre­
quencies greater than 50 % , whi1e S. agilis had a frequency greater than 20%.
These 1 0 species comprised 88% of the Pacific sand fauna.
Six species were found on both coasts : the po1ychaetes Seolelepis agilis,
Hemipodus armatus, and Sthenelais maeulata; the isopods Cirofana salvadoren­
sis and Exosphaeroma diminutum; and the amphipod Orehestoidea biolleyi.
The presence of these . species contributed to an average index of faunal affinity
of 12.6 between the Pacific beaches compared with the At1antic beaches (Fig.
1 ) . Of the total species present, crustacea comprised an average of 5 5 % of
the Atlantic fauna (range of 42-100% among the individual beaches) and
43 % (range 40-54%) of the Pacific; annelids 24% (range 0-37 % ) of Atlan­
tic and 2 5 % (range 29-3 3 % ) of the Pacific fauna; mollusca 9 % (range
0-2 5 % ) of At1antic andli 19 % (range 0-33 % ) of the Pacific fauna; and aH
other taxa 12 % (range 0-14 % ) of Atlantic and 1 3 % (range 0-15 % ) of the
Pacific: fauna.
There were significant differences between the At1antic and Pacific
sandy beaches in density, numbers of species, and grain size. Mann Whitney
U tests (SIEGEL, 1 3 ) showed that the density of organisms was significant1y
greater ( p = 0.00 1 ) on the Pacific beaches than on the Atlantic beaches ;
that the number of species was significant1y higher (p= 0.0 1 ) on the Pa-
DEXTER: SANDY·BEACH FAUNA OF COSTA RICA AND cotoMllrA
55
cific beaches ; and, that median sand grain size was significantly higher ( p =
0.05 ) o n the Atlantic beaches. The Shannon-Wiener diversity indices on both
coasts (Table 3 ) ranged from about 0 . 5 0 to 2 . 5 0 ; no consistent differences
between the coasts were found. The evenness of distribution of individuals
among species (as measured by NM) was low on aH sandy beaches on both
coasts (TabIe 3 ) .
Exosphaeroma diminutum oa the Pacific coast had significantly higher
den sities on lighter calcareous and quartz sands, compared to darker vo1canic
sands. It was present on the Atlantic coast only on ca1careous beaches, and
was distributed throughout the intertidal zone on both coasts.
Ciro/ana salvadorensis occurred on aH substrate types and sand grain sizes
on both coasts. However, it dominated the fauna when grain size was Iarger
than 300 fL. It was most abundant in the high and mid tidal levels.
On the Pacific beaches, S. agilis was more abundant (average density
of 721m2) on volcanic sand beaches; it had low densities or was absent
(average 11m2) from ca1careous and quartz beaches, and had low densities
ave rage 61m2) on calcareous beaches on the Atlantic coast. It was distributed
throughout the intertidal zone with greater densities toward the lower levels.
Predominantly low tide species included Hemipodus armatus, Nephthys
singularis, Ancinus brasiliensis, phoxocephalid amphipods, Emerita brasiliensis, E.
rathbtmae, Donax panamensis, D. denticu!attJS, Olivella semistriata, and boda­
triid cumaceans.
DISCUSSION
The beaches in Costa Rica and Colombia varied widely in several
physical factors, among which sediment composition and mean particle size
were examined. The three main sediment types were ca1careous sand, quartz
sand mixtures, and vo1canic-igneous sands. Since the latter are usually dark
in color, calcareous sands usually light, and quartz sands of a medium color,
differences in heat retention capabilities might be reflected in faunal compo­
sitian and/o! abundance. Although some species appeared to change densi­
ties in relation to sediment composition, no overall trend was evident. Num­
ber of species and density of sand fauna did not appear related to sediment compo­
sition. The influence of sediment composition upon sandy-beach fauna is not
yet apparent.
Beaches with the highest degree of faunal affinity on the Atlantic coast
were Airport Beach, Calmita Sóuth, and Puerto Viejo, Costa Rica, and Puerto
Colombia, Colombia. These beaches were widely separated geographically, na­
row to wide, of calcareous or igneous sand, of fine to medium grains, and
organism density ranged from low to high. The only obvious feature shared in
cornmon among these beaches was an abundance of or dominance by the iso­
pod C. salvadorensis. On the Pacific coast, Espadilla, Sámara, Playita Blanca, and
Tamarindo, all in Costa Rica, had the highest affinities. The beaches on the
Pacific were composed of fine sand, either calcareous or quartz, and were
Vt
CA
TABLE 1
Distl'ibution and density (NQ 1m2)
1 sandy-beach speeies on the Atlantie coasts
0
1
0
Costa Rica and Colombia
Name and
o
•
'.s
c �.
o U
¡:Q _
c:
C"J 'o
� 8
P: ;.::i
'"
'v
....
"d
c:
<:
c:
'"
Vl
Species
..a
N
.
�
�
QJ
•
¡:Q u
.....
....
..
c:
o 'o
fr 8
<i ;.::i
P'i
�n
site number
P'i
'" .
.-:: U
'" ,
.-:: U
", ..a
u �
o
Z
U "5
::l
..a
- ""
::l
V"\
_
..a
", .r::
o
Vl
�
.s
0
....
�
Ó 'D
tl... 'v
:>
o
o
",el
QJ r--
�
8
o
ro
.... . �
QJ ..Ll ca
�
;;J 8
tl... o
-O
U
ti)
o
¿
1::
�
�
Nematoda
ScoJeJepis agilis
Hemipodus a1'1natus
.4
17 . 5
12.5
14.4
1 .4
.6
5 .7
.4
.8
4 .4
,5
1 .7
1.1
.4
1 0 .4
9.6
.4
1.0
Pisionidens indica
2 1 .3
1 .4
Sthenelais macula/el
.7
Paraonides sp.
2.9
Ceratonereis mirabilis
2.4
Oligochaeta
Cumacea
Bodatriidac
.
1 .4
4
Crustacea: .Isopoda
Exosphaeroma diminuttlm
Cirolana pat'va
.8
2. 9
1,4
4.6
2.5
Cirolana saJ'Jadorensis
31.3
196.3
3.3
178.6
36.7
Ancinus bl'asiliensis
63.3
.8
2.2
4.8
1.1
<:
Cñ
;!
37 . 1
O
Cl
;;
;J
O
:!l
�
t-'
.4
Lumbrine1'eis sp.
g;
O
t-'
.4
Polychaeta
0\
t1
tt1
o:J
.6
Nemertea
Crustacea :
�'"
57.1
18.3
Crustacea: Amphipoda
Phoxocephalidae
Atylus minikoi
O"chestoidea ?biolleyi
Haustorius sp.
01'chestia ?f ritzi
Photiidae
Crustacea: Tanaidacea
Leptochelia sp.
�
Crustacea : Mysidacea
Bowmaniella diisimilis
Crustacea : Decapoda
Emerita brasiliensis
HiPpa cubensis
Ocypode quadrata
Lepidopa richmo1ldi
brachyuran megalops
Insecta
Coleoptera larva sp. A
Coleoptera larva sp. B
Mollusca: Bivalvia
Donax demiculatus
Tivella mactroides
Mollusca: Gastropoda
Terebl'a cinerea
1.1
.8
1 .0
.6
tJ
t-"
:><:
1 5 .0
4.2
�
�
1 .3
en
.6
.4
.4
.8
1.7
.5
.5
.4
.4
.4
�
O
�
iP
2 9
tT1
>(")
1.3
'ti
>-
.8
.4
.4
.6
L5
te
�
O
'ti
1 .3
(")
O
rn·
.4
.4
>-i
>i:>ó
ñ
.5
>-
.4
14.4
66.8
.7
.6-
.7
71.3
>-
Z
O
(")
O
t-<
O
;;::
trJ
¡;
VI
�
TABLE 2
Distríbutíon a/ld densíty (NO¡m2)
Ut
co
01
sandy-bea.h spedes on the Padfic .oasts of
Costa Ri.a and Colombia
Name and site number
'"
g
u
¡x¡
I"Í
I"Í
U
1i u
o�
.�
lO
>- o
..;:1 U
�
Nematoda
p:¡
p::
o'
"O N
e
. ;::
"
8
'"
t-<
Species
Platyhelminthes
U
U
"," «"\
...'"
8
-'"
(f)
Seolelepis agilis
Hemípodus arma/m
N ephthys singularis
Ch01ze minuta
Sac.oeirrus sp.
Pisione rem o ta
O rbinía johnsoní
Phyllodoce sp.
Armandía sp.
Magelona ríojai
Sthenelais mamlata
. Euzonu, furcif�rus
Arzaitides ?multiseriata
I"Í
�U
n
�
'" ...
�
"<1'
Ec
�
u
o
ed'" 1('\
u
e
¡:Q ...
�
'"
;:J
U
'
-o
u
�
'"
- I"Í
I"Í
\O
'"
U
'"
>'"
-.
,,>
o
0..
Q.)
;:J
� CI
>-.
U
;:; �•
�U
¡:Q
.4
"O
r--
tt U
U3 o
'" fr
>- ;:J
v)
'"
¿; CI
o'
u
00
'"
o '"
'"
e
;:J
>-.
>
t1
tti
.3
3 .8
g;
<!
¡¡;
..;
.3
38.6
Nemertea
Polychaeta
", U
§
� a
2 5 1 .0
.7
13.7
1 1 .9
1 1 .0
1.4
5 .7
.3
70.0
1.1
1.1
6.3
3.3
.5
3.7
.4
1 .4
30.0
1 .0
1.0
ñ
>
...
.4
.7
20.4
.5
.7
.4
1.7
.3
O
O
:;
..;
'"
O
."
3.0
17.6
b:l
(5
1-'
.8
.5
1.1
.6
Crustacea :
Amphipoda
Phoxocephalidae
Megalt¡ropus sp.
OreheJloidea ?biolleyi
AeanthohaustoriuJ n. sp.
1 3 2 .0
23.3
2.2
145.2
280.0
122.3
.5
1 .9
2 5 .7
unid entified amphipod
Synehe/idii¡m sp.
533.3
Bodatriidae
198.7
2.9
.5
unidentified cuma'tean
Crustacea : Isopoda
Exosphae1'Oma diminu/flm
eirO/allá sa/vadorensis
27.7
1 5 5 2 .9
206.2
446.3
364.8
27.0
1 .9
622.9
Crustacea :
Anomuran megalops
Brachyuran megalops
Uea sp.
>-
(')
::c
3::>.6
23.0
.."
86.3
.6
1 1 33.3
5.0
42.1
81.1
85.2
44.4
9.3
18.3
6.7
>e
�
o
.."
(')
4.3
o
en
.5
...¡
>-
20.0
�
(')
Decapoda
Emerita rathblmae
LePidopa mexicana
Oeypode óeeidetltaJis
ArenaeuJ 7IIeX1calZ1iJ
�tJ;
tyj
.2
Crustacea: Mysidacea
Bowmaniella sp. A
Bowmaniellct sp. B
Bowmaniella sp. C
.Metamysidopsis sp .
tT1
�
>-
11
1 .0
tl
tT1
><:
'-l
en
.7
Corophiidac
Crustacea : Cwnacea
1.1
>-
1 1 .4
2.7
3 1 2 .4
1.1
.5
4.8
.3
1.1
.7
.6
.7
.4
.�
4.4
�
tJ
(')
O
t-'
O
�
tl1
1.1
.4
1.1
3.3
:;
v.
\O
TABLE 2 ( Cont. )
Distribution and density (NQ /mf) oi Jandy-beach spedes
Oll
�
the Pacífic cotlslJ oi
Cosla Rica and Colombia
Name and site number
¡::¿
os
u
; ¡::¿
iii u
.5
.�
..
Species
o�
u
!
8
Po.
¡::¿
P:::
U
U
o
"O '"
c:
.�
'"
"," «"\
...
'"
E
t/)
-'"
�
�
¡::¿
", U
§
Po.
�
c:..
'" �
>4 .5
c:
�
Po.
� U
�
�
el
� �
a:l ...
r!
'"
a:l
- ¡::¿
¡::¿
If"'\
U
.¿
u
gu
\D
U
<n" r'" o
>-' 0.
'" <!J
- �
Po.
CI
oS
......
7.4
Donax panamensis
7.3
10.5
>-. �
� CI
o'
u
..
O '"
c::
'"
�
......
.9
Donax dentife,
Dona:, f!.racilis
1 .0
Olivel/a semistríata
.7
7.6
Natiea chemnitzi
.3
Agarollia te,stacea
2.3
4.0
�.
<
¡¡:;.
43 1 .7
1 .0
13.8
1.[
Echinodermata: Echinoidea
Mellita longifissa
.5
Ophione.ma sp.
.5
Chordata
4.8
O
m
el
3 .7
2.3
3
.7
.2
.7
.2
O
1'"
O
G)
:;:
;j
O
6.7
.5
'd
§
t-
Na/iéa unífasda/a
Ophiophragmm sp .
2.2
1 .0
Hastula luctuosa
Ophiuroidea
1 .9
1 .0
4.3
Strigil/a cicercula
Mollusca: Gastropoda
54.4
1.1
Donax navicula
Branchiostoma
'" fr
o;
�
MoIlusca: Bivalvia
Echinodermata:
U
'"
:=:i P:::.
"' u
o.
� o"
"O
1.1
DEXTER: SANDY·BEACH FAUNA OF COSTA RICA AND COLOMBIA
61
dominated b y the isopod E. diminutum. Width of beach and density of fauna
varied extensively. Factors influencing higher faunal affinity have yet to be
identified.
The overall faunal similarity among the beaches was low; only 1 8 %
of the Atlantic species and 1 9 % of the Pacific species were found on at least
haH of the beaches examined on their respective coastlines. This indicates
some flexibility in sand beach faunal composition. The variation in faunal
components is not easily related to geographical location, sand composition,
particle size, nor density of the fauna.
The six species which were common to both coasts coostituted 68 %
of the total fauna by oumber. The isopods C. salvadorertsis and E. dimtnu­
tum together contributed 62 % of the numerical composition of the fauna. Four
of these amphi-American species were found on the maj ority of the beaches.
C. sahltldorensis occurred on 17 of 18 beaches studied, S. agilis on 16 of 18
beaches, E. dim}nutum on 1 3 of 18 beaches, and H. armatus 0 0 1 2 of 1 8
beaches. These factors, abundance and ubiquity, resulted in an indcx of affí.
nity of 1 2.6 between the Atlantic and Pacific beaches, a rather high figure,
considering that only 1 % of the total species studied were common to both
coasts.
The faunas of the tropical American coasts of the Pacific and Atlantic
are similar and closely related. The same species are dominants on both coasts,
and abundant organisms are cognates, belonging to the same genera. The ma­
j or difference between the faunas is the 7-fold difference in average density.
A 6-fold difference in density and a 9-fold difference in biomass was found
between a Pacific and an Atlantic Panamanian sandy beach ( DEXTER, 3 ) .
Two explanations for this density difference are proposed. M...ARTIN,
et al., (9 ) characterized the Pacific coast of Panama as having 3-5 times the
benthic biomass and 2-5 times the primary productivity of the Atlantic side.
If this difference in productivity extends northward and southward, then per­
haps food availability is a significant factor in limiting intertidal density on
the Atlantic beaches.
A second explanation is the rigorous physical environment. Physical
Pacific and Atlantic coasts of tropical America. The
Pacific coast is characterized by latge tidal amplitudes and two regular tides
daily, and the fauna of the Pacific is exposed to greater ranges in temperature
and salinity (9) .
The tidal cycle on the Atlantic coast is mixed, wi�h on�
or two tides occurring irregularly. The irregularity of the Atlantic tidal regimes
sometimes results in considerable mortality among intertidal organisms ( 6 ) .
During the dry season Atlantic beaches become high energy environments with
considerable wave action, and thus have coarser sediments ( 7) . Coarsé sedi­
ments and extended periods of desiccation both could contribute to limitatiol1s
in abundance and probably also reduce number of species .
{actors vary between the
Peracaridans numerical1y dominate sand beach faunas of tropical Ol.nd
REVISTA DE
62
BIOLO(;IA
TABLE
TROPICAL
3
StTucture of sandy-beaeh fauna of Costa Rica and Colombia
4-<
o
�
-;;
Si te
"'"
v
�
v
..D
;:J 'T1
;:J
Z .9
CL
8
'O
.... ;:J
V -u
..D . �
8 . ::;
"
'-'
c:
V
�
8
'E
Z s;.
'"
'"
", ---
f:: °8
<G ---
:>- '"
�
.�c:
o-
v Z
0 ---
>:
<lJ
�
Z
---
f3 .S
>:
0
CJ
c:
o :�
'"
.�
---
;:;::
'1J
6 :>-
a E
C\l ;;..
.c . �
(/) v
ti
ti;
�
c:
15
v
u
....
v
p...
Dominant organisms
:�
o
o..
§
u
ATLANTIC BEACHES
San Andrés
Playa Bonita
Aúport Beach
Cahuita North
CaImita Soutb
Puerto Viejo
Cartagena
9
3
1.2
8
274
7
2.4
1 14
511
7
8
51
n.e.':'
1.51
.26
2 .4
213
0.50
.08
1 .8
28
n.e.
.27
407
12
2.1
194
0.64
.02
102
9
1 .8
57
n.e.
.09
12
371
Puerto Colombia
Santa Marta
n.c . *
2.8
133
168
8
2.8
60
356
15
2 .4
148
1 .96
.15
n.e.
.01
2.51
.21
None
Ancimls brasiliensis
56
Cirolana salvadorensis
27
Scolelr:pis agilis
15
Cirolana salvadorensis
92
Scolelepis agilis
51
I-ie:nipodus arma!us
16
CirolclIla salvadorellsis
12
Cirolcllla salvadorensis
92
ClrolallCl salvadoreizsis
64
Donax dentÍ'culatus
26
Donax denúeulatus
48
Cirolana salvadorensis
28
Phoxocephalid amphipods
11
Cirolana salvadol'ensis
95
Donax denticulatus
48
Pisionidells indica
14
Cirolana salvadol'emis
12
Exosphaeroma dimillutum
79
PACIFIC BEACHES
Playita Blanca
Tamarindo
15
2 5 40
Sámara
Puntarenas
de Barranca
Boca
13
4116
2.1
3.0
1960
847
1.20
1.91
.07
. 14
944
15
2.1
450
1.25
.08
2 588
10
2,1
1218
1.65
. 17
548
16
2 .7
203
2 .44
.19
Cirolana salvadorensis
11
Exosphcleroma dónillutum
53
Bodatriid cumaceans
Phoxocephalid amphipods
24
Exosphaeroma diminutum
81
Cirolana salvadorensis
51
Emerita l'athbullae
26
Seole/epis af!.ilis
21
Scolelepis af!.ilis
35
Donax
Jacó
1 373
Cocal
1 0 34
16
4.8
215
1 .78
Espadilla
Juan Chaco
2 587
12
2.1
1231
2047
14
1.8
1 1 37
*
n.c.
22
3 .0
458
1 .97
.10
panamensis
27
Exosphaeroma diminutum
18
Cirolana salvadorensis
11
Phoxocephalid amphipods
61
Exosphaeroma diminutum
19
.1 2
Phoxocephalid amphipods
57
Cirolana salvadol'ensis
20
0.47
.02
Exosphael'oma diminutum
92
1 . 76
.13
Aea1Zthohaustol'ius
Donax . f!.l'acilis
not caIculated,
16
n.
sp.
48
, 38
DEXTER:
SANDY·BEACH FAUNA OF COSTA RICA
At'\¡1) COLOMBIA
63
sorne temperate beaches ( 3 ) , and comprise 68 % of the Atlantic and 7 5 % of
the Pacific Costa Rican and Colombian sand fauna in this study. AH pera­
caridans have direct development with young released from the brood pouch
as small juveniles, Direct development should tend to limit dispersal ; how·
ever, the two most abundant tropical sandy-beach peracaridans, Cil'Oiana salva·
dorensis and Exosphael'oma diminutum, occur on both coasts, The biology
of these two species should be examined to determine which factors contribute
to their success as dominant sand beach organisms.
The taxonomic status of the dominant sandy-beach isopod Ciro/ana sal­
t1adorensis is currently being clarified (GLYNN, DEXTER, and BOWMAN, manu­
script submitted for publication) . This abundant species has been described as
Exci1'OIanCi b1'asitiemiJ, Cirofana keopckei, and Ciroiana salvadorensis. The name
Excirotcma brasitiensis has taxonomic priority.
ACKNOWLEDGMENTS
This research W'as sponsored by the Organization for Tropical Studies,
lne. grant N9 F70-47. The author wishes to thank the following individuals
for their help in the identification of the fauna : Lawrence Abele ( decapod
( Amphipoda),
Crustacea) , A. D. Ansell (Donax species), E.L. Bousfield
Thomas B owman (Mysidacea), Robert Bullock (Mollusca), John Dearborn
( Ophiuroidea), Thomas Ebert (Echinoidea), Kristian Fauchaid ( Annelida),
Robert Given ( Cumacea) , Peter Glynn (Isopoda), James McLean (Mollusca),
and Charles Messing (Tanaidacea) . Richard Berry determined the geological
composition of the sand.
RESUMEN
En un estudio sistemático de las comunidades de las playas arenosas
de ambas costas det Costa Rica y Colombia, desde febrero a mayo de 197 1 ,
se colectó 3 3 especies y 2,249 individuos en el litoral del Atlántico, y 5 2 es ­
pecies y 17,747 individuos en playas del Pacífico.
La fauna del Atlántico estuvo dominada por los isópodos C.iJ:.Qlana
salvado1'ensis y Ancinttr b'rasiliensis, los poliquetos Scolelepis agil!s y HemiPodltS
arma!uJ, anfípodos foxocefálidos, y el decápodo Emerita b1·(J'siliemis. La fauna del
Pacífico estuvo dominada por los isópodos C. salwdoi'ensis y Exosphael'oma dimi­
nutu1JZ, los poliquetos S agilis, H. arma /us, y Nephthys singularis, anfípodos
foxocefálidos, el decápodo Emel'ita rathbunae, un cumáceo bodatrído, el bivalvo
Donax panamensis, y el gastróoodo Olivefla semistríata.
.
La fauna del Pacífico se caracterizó por una mayor densidad y más especies
que la fauna atlántica, Las especies más abundantes, C. salvado l'ensis y E.
dimintttu1n, fueron halladas en la mayoría de las playas de ambas costas.
LITERATURE ClTED
1.
DAHL, E.
1 9 5 2 . Ecology and zonation of sand beaches.
Oikos 4:
1·2,.
REVISTA
64
2.
DE
BIOLOGIA TROPICAL
D . M.
DE XTER,
Strueture of an intertidal sandy-beach community io North Carolina.
1969.
Chesapeake Sci., 1 0 : 93-98.
3.
4.
DEXTER,
Comparison of the eommunity structures in a Pacifie aod an Atlantie Pa­
namanian sandy beach. Bull. Mar. Sci., 2 2 : 449-462.
EMERY,
K. O.
Rapid method of meehanieal anaIysis of sands. J. Sed. Petrol.,
1938.
5.
FAGER, E .
GLYNN,
1968.
7.
LLOYD,
1 964.
Amer. Nat.,
106:
293-3 1 0 .
P. W.
Mass mortalities of eehinoids and other reef fIat organisms eoineident with
midday, Iow water exposures in Puerto Rico. ¡Har. Bio/. ( Ber/in ) , 1 : 2 2 6-243.
P. W.
O servations on tbe eeoIogy of tbe Caribbean and Paeifie coasts of Pana­
ma. Bull. Bio/. Soco Wash. 2 : 1 3 - 20.
M., & R. T . GHELARDl
A table for eaIcuIating the "EquitabiIity"
J. Anim.
9.
105-1 1 1 .
GLYNN,
1972 .
8.
8:
W.
Diversity: a sampling study.
1972.
6.
D . M.
1972.
MARTIN,
1970.
Eco/.,
33:
component of speeies diversity.
37 3-449.
W. E . , ]. A. DUla, S. G. BLOOM, & J. T. MCGINNIS
Possible effects of a sea-leve! canal on the marine eco!ogy of ¡he American
lsthmian
dies,
Region.
Bioenvi1'Oilmental
Atlantic-Pacific
Iumbus, Ohio,
Fig. 1.
219
imeroceal1ic
and
cana!.
radi%
gical-safety
feasibililY
SIIl­
Battelle Memorial Institute, Co­
pp.
Pereent of beaehes in cIasses of fa¡'lOaI affinity
among intertidaI sandy-beaeh eommunities of Atlan­
t.i e and Paeifie coasts of Costa Rica and Colombia
witb comparison among AtIantie beaehes ( 28 paiIs ) ,
Paeifie beaehes ( 3 6 pairs) and bctween AtIantie
and P-acifie beaehes ( 7 2 pairs ) .
DEXTER:
SANDY-BEACH
FAUl'<A
OF
KEY
COSTA
RICA
AND
COLOMBIA
Average index va l ue
At l ant i e Beaehes
39 . 7
Pae i f i e Beaehes
26 . 5
At l a n t i e -Pae i f i e
Beae hes
12.6
I N D I C E S O F AF F I N I T Y B E TW E E N BEAC H E S
..
1
65
REVISTA DE BIOLOGIA TROPICAL
66
10.
RODRIGUEZ,
G.
1959.
marIne
The
communities o f Margarita
Island,
Venezuela.
Btdl. Mar. Sci.
Gulf Carib., 9 : 2 37·280.
1 1.
SANDERS,
1960.
L.
H.
Benthic
studies
12.
S.A.NDERS,
1968.
1 3.
SIEGEL,
1956.
W ADE,
1967.
B uzzard s
IIl.
Bay.
Oceallogr.,
5:
The
structure
of
the
soft·bottom
138· 1 5 3 .
H . L.
Marine henthic cliversity:
a comp arati ve study.
Amer. Nat., 1 0 2 : 243·282.
S.
Nonparallletric stati.rtic.r for the behen'ioral .rcience.r.
New
14.
in
Lilll llo1.
community.
McGraw
Hill,
York .
B. A .
DOllax denticulatus
Bull. Mar. 5ci. Gul¡ Carib., 1 7 : 149·174.
Studies o n the biology of t h e West Indian beach clam,
Linne.
Ecology.